function $ajax({
    url,
    success
}){
    var xhr = new XMLHttpRequest()
    xhr.open('get',url,true)
    xhr.send()
    xhr.onreadystatechange = function(){
        if(xhr.readyState===4&&xhr.status>=200&&xhr.status<300){
            var res = JSON.parse(xhr.responseText)
            success(res)
        }
    }
}